1. Technical Field
The field of invention is lead-acid storage batteries. More particularly, it relates to an improved alloy for producing side terminals for these batteries.
2. Background Art
A lead alloy commonly used to make terminals for lead-acid storage batteries is composed of 2.75-3.25% antimony, 0.05-0.20% arsenic, 0.15-0.40% tin, 400-600 ppm copper, less than 30 ppm sulfur and less than 20 ppm selenium. Actual composition specifications for the referenced alloy are those placed into the caster, rather than the finished bushing composition. When parts were produced by gravity casting at temperatures typically above 800.degree. F., this necessitated the use of grain refiners (Cu, S, and/or Se) for suitable metallurgical structure. When parts are produced via a die casting process typically at temperatures below 800.degree. F., such grain refiners (Cu, S, and/or Se) form dross and are reduced or completely lost from the finished part. Unwanted reductions in other alloying elements can occur as dross forms. Drossing losses are an expense that is figured into the bushing cost.
Side terminal bushing properties that are important to safety and functional performance are nut rotation, weldability, weld torque, age hardening, and corrosion resistance. Particularly in hot climate areas which accelerate corrosion processes, improved corrosion resistance is desirable for extended product life and performance. A hypothesis of corrosion sensitivity was developed, which involves the composition of the bushing alloy, welding temperatures (particularly at the lead-to-poly interface), and catalytic or protective interaction of alloy components in the degradation of polypropylene container, and associated lead alloy corrosion due to the interaction of polypropylene decomposition products and lead alloys.
Thus, there is a need for an improved alloy for manufacturing terminals in lead-acid storage batteries.
The objects of the invention therefore include:
a. providing an alloy for manufacturing terminals for lead-acid storage batteries which have reduced drossing during die casting operations; PA1 b. providing an alloy of the foregoing type which reduces material losses and cost of recycling; PA1 c. providing an alloy of the foregoing type which has improved composition stability due to reduced pull-out of alloy components; PA1 d. providing an alloy of the foregoing type which has improved compatibility with polypropylene at elevated temperatures by reducing copper, which catalytically oxidizes polypropylene and increasing tin, which provides anti-oxidant protection to polypropylene; PA1 e. providing an alloy of the foregoing type which has improved grain refinement for the terminal weld joint; PA1 f. providing an alloy of the foregoing type which has improved intrinsic corrosion resistance; PA1 g. providing an alloy of the foregoing type which has improved corrosion resistance when assembled into a finished battery. PA1 h. providing an alloy of the foregoing type which has improved tolerance to high temperature welding conditions; and PA1 i. providing an alloy of the foregoing type which retains minimum void volume, acceptable nut rotation torque, weld torque, and weld current range.